The present invention relates to the technical field of hotmelt adhesives and their use in corresponding assembly or bonding procedures, and also of the hotmelt adhesive discharge apparatuses employed in this context, especially in the form of hotmelt or hot glue guns.
The present invention especially relates to a stick-type (stick-shaped, rod-formed) hotmelt adhesive body, especially hotmelt adhesive stick, based on a reactive hotmelt adhesive and on a cleaning or purging agent, the hotmelt adhesive body being preferably in cylindrical form and being suitable especially for use in hotmelt glue guns.
The present invention likewise relates to a method for producing the hotmelt adhesive body, especially hotmelt adhesive stick, according to the invention, and to the adhesive body as such that is obtainable by the method.
The present invention relates, moreover, to a hotmelt adhesive discharge apparatus (hotmelt adhesive processing apparatus), especially in the form of a hotmelt or hot glue gun, which comprises the hotmelt adhesive body, especially hotmelt adhesive stick, of the invention, and also to a kit based on a hotmelt adhesive discharge apparatus, especially hotmelt or hot glue gun, on the one hand and on a hotmelt adhesive body, especially hotmelt adhesive stick, according to the invention, on the other hand.
The present invention relates, furthermore, to a pack unit or container which comprises at least one hotmelt adhesive body, especially hotmelt adhesive stick, of the invention.
The present invention, furthermore, relates to a use of the hotmelt adhesive body, especially hotmelt adhesive stick, according to the invention for and/or in assembly and/or bonding processes or the like.
The present invention additionally relates to a use of a coloring component or colorant for identifying or providing a visual or optical difference between sections on which the hotmelt adhesive body according to the invention is based, with the respective sections comprising a reactive hotmelt adhesive on the one hand or else a cleaning or purging agent on the other hand.
Lastly, the present invention also relates to the method for identifying or providing a visual or optical difference between the aforesaid sections of the hotmelt adhesive body according to the invention on the basis firstly of the reactive hotmelt adhesive and secondly of the cleaning agent.
Hotmelt adhesives, also referred to synonymously as hot-applied adhesives, hot glues or hotmelts, are in general products which are solvent-free and are solid at room temperature, which on heating or in the hot state take on a fluid or liquid state, so that on this basis application may be made to a bond area. On cooling, with an associated consolidation of the hotmelt adhesive, a solid and permanent (adhesive) bond is then developed.
The hotmelt adhesives on which this system is based are provided generally in the form of stick-type hotmelt adhesive bodies, also referred to synonymously as hotmelt adhesive sticks or hotmelt glue cartridges, which are intended in particular for processing in corresponding hotmelt adhesive discharge apparatuses, such as hotmelt or hot glue guns. In this connection, the hotmelt adhesive bodies generally have a cylindrical form with a defined cylinder height (i.e., with defined length of the hotmelt adhesive body) and with a defined, more particularly circular, base area (i.e., with defined diameter of the hotmelt adhesive body).
Hotmelt adhesives are generally associated with the advantage of rapid processing in conjunction with low material price, and also allow bonding of a very wide variety of materials and substrates. Also of advantage in this context is that the hotmelt adhesives used allow any unevennesses in material surfaces to which bonding is to take place to be compensated, with the resulting bonded joint or bonded layer also exhibiting a certain elasticity.
Against this background as well, hotmelt adhesives are used generally in numerous industrial applications, such as, for example, in the packaging industry and also in the automotive, furniture, and woodworking industries, employing corresponding laminating techniques, for example. In the electrical engineering sector as well, hotmelt adhesives find far-reaching use, as for example for mechanical stabilization, insulation, and bonding of corresponding components. Furthermore, hotmelt adhesives are often used in the domestic sphere or home hobby and craft sector, but also in floristry and in the packaging industry.
Against the background of the extensive use and of the numerous applications of hotmelt adhesives in both industrial and domestic spheres, as well, there is a great demand in the art for further optimization in relation to the adhesive systems employed accordingly.
Generally speaking, in the art, hotmelt adhesives are processed or applied using corresponding discharge apparatuses, such as, in particular, hotmelt or hot glue guns. The product portfolio available for hotmelt glue guns is divided into various fields of application, according to the profile of technical requirements. Tank glue guns without compressed air, with compressed air, and tank guns for cartridges are prevalent.
Also established in particular, because of their favorable price/performance tradeoff and their ease of handling, are hotmelt or hot glue guns for hot glue sticks. Here, generally, a hotmelt adhesive in stick or cylinder form is introduced on the rear side of the hotmelt glue gun, and in the interior of the hotmelt glue gun it is heated by a heating or melting facility, which in particular is electrically operated, and is thereby melted, or converted into a fluid or liquid state. Continued mechanical infeed of the still-solid hotmelt adhesive into the heating or melting facility causes the fluidized hotmelt adhesive present there to be moved on accordingly and discharged through a discharge facility, more particularly an adhesive nozzle or the like, which may be part of the heating or melting facility, and it is applied to an article to be bonded. The transport of the hotmelt adhesive, especially in stick form, is ensured here generally by a corresponding transport mechanism, which in particular is manually actuated.
In this connection, WO 2008/101455 A2, or DE 10 2007 008 722 A1, which belongs to the same patent family, relates to a hot glue or fast-bond gun having a gunlike housing, the construction of the gun being such that the hotmelt adhesive to be processed can be guided through the hotmelt glue gun at variable speed; in this connection, the heating power can be adapted for melting the hotmelt adhesive.
One of the disadvantages of the hotmelt glue guns generally used in the processing of hotmelt adhesives, however, is that after application or processing of the hotmelt adhesive, adhesive which has already melted remains, particularly in the region of the heating or melting facility and of the discharge apparatus or adhesive nozzle, where it hardens. This is a problem particularly in view of the reactive hotmelt adhesives, described hereinafter, since these adhesives, by virtue of their chemical postcrosslinking and also of the development of chemical adhesive bonds, undergo irreversible hardening, so to speak, and do not form dissoluble adhesive bonds even when exposed to heat. A possible consequence of this is that hotmelt glue guns which are not freed from residual hotmelt adhesives or cleaned immediately after use become unusable, or before renewed operation must be taken apart and cleaned, which is costly and inconvenient.
The art is aware in general of two kinds of hotmelt adhesives, namely those referred to as nonreactive hotmelt adhesives, on the one hand, and the reactive hotmelt adhesives, on the other:
Frequently used in the prior art, accordingly, are nonreactive hotmelt adhesives, of the kind based, for example, on ethylene-vinyl acetate (EVA) and polyesters (PES). Nonreactive hotmelt adhesives of this kind are used for a multiplicity of standard applications on the basis as well of their attractive price/performance tradeoff. The chemical basis of adhesives in stick form is therefore ethylene-vinyl acetate (EVA) in particular. To lesser an extent, alongside the use of polyesters (PES), there are also hot glue sticks available that are based on polyolefin (PO) or polyamide (PA). The aforementioned sticks are fundamentally homogeneous in terms of their chemical composition.
The fields of application for EVA sticks, for example, are to be found primarily in the sphere of floristry and the packaging industry. The polyamides are employed in the automobile and electrical industry sectors.
Nonreactive hotmelt adhesives are notable in particular for short open times and setting times. Here, a central bonding principle of nonreactive hotmelt adhesives is that the actual bonding is essentially physical, resulting from the consolidation of the adhesive that is present on the cooling of the discharged hotmelt adhesive. Consequently, the adhesive systems in question that are based on nonreactive hotmelt adhesives do all in all enjoy very good handling properties, but do not always enjoy ideal bonding properties, because of the purely physical bonding.
With regard to the nonreactive hotmelt adhesives, it should also be said in this respect that after consolidation has taken place, they can in principle be melted again; this indeed facilitates the ease of handling in hotmelt glue guns, since these guns, even during relatively long pauses in operation, do not, so to speak, become “clogged”, but it is disadvantageous in respect of the bonding properties as such, since adhesive bonds that have developed are occasionally not sufficiently heat-stable. As a result, therefore, the nonreactive hotmelt adhesives in question are not always sufficiently heat-resistant.
In this connection, nonreactive hotmelt adhesives also sometimes have the disadvantage that their mechanical dimensional integrity is low and that they tend to exhibit creep even under relatively low static loading and at relatively high ambient temperature. For this reason as well, nonreactive hotmelt adhesives have only a small usage range in applications particularly at above room temperature. Moreover, especially after they have been processed, nonreactive hotmelt adhesives are occasionally not always adequately resistant in chemical terms.
As well as the nonreactive hotmelt adhesives referred to above, there are also reactive hotmelt adhesives known in principle in the prior art, as formed, for example, on the basis of reactive polyurethanes or, for example, silane-modified polyolefins.
A particular feature of the reactive hotmelt adhesives is that they possess chemically reactive functional groups which, in particular during and after processing or application, under the influence, for example, of heat, radiation or moisture, lead to (post)crosslinking and/or, further to the physical bonding properties, to the development of chemical adhesive bonds.
In the processing or application of reactive hotmelt adhesives, therefore, following application to articles to be bonded, there is not only a physical setting but also, in conjunction therewith and/or subsequently, a further chemical reaction to form high molecular mass polymers with high cohesion, and/or to form additional adhesive bonds due to chemical reactions with the surface of the articles to be bonded. In this way, with reactive hotmelt adhesives, it is possible to achieve very good bonding properties, high temperature stabilities in conjunction with good low-temperature flexibility, and also high resistances to a multiplicity of chemicals. Reactive hotmelt adhesives therefore have not only the advantages of the aforesaid quick-setting nonreactive hotmelt adhesives but also those associated with the chemical crosslinking and formation of chemical adhesive bonds. In particular, reactive hotmelt adhesives, owing particularly to the postcrosslinking, exhibit, so to speak, initial physical curing and, equally, rapid processes of processing without long-drawn-out drying phases.
Reactive hotmelt adhesives, in particular, have good bonding properties and high temperature resistances insofar as, owing to the chemical postcrosslinking and the development of chemical adhesive bonds, a reactive hotmelt adhesive cured accordingly can no longer be melted by exposure to heat, or the adhesive bonds formed cannot be parted by heating.
Against this background as well, however, in their storage and in their processing especially in hotmelt glue guns, reactive hotmelt adhesives are problematic, since, on the one hand, excessive contact with, for example, (atmospheric) moisture or (ambient) radiation leads to unwanted, premature reaction of the chemically reactive groups of the hotmelt adhesive. On the other hand, in the case of processing in hotmelt glue guns, reactive hotmelt adhesive, previously melted, and remaining in particular in the region of the heating or melting facility and also of the discharge facility, especially adhesive nozzle, may undergo (thermally) irreversible curing in the event of a pause in operation or standstill and, in so doing, may enter into chemical adhesive bonds with the inside surfaces of the hotmelt glue gun that are in contact with the reactive hotmelt glue, such bonds being impossible to part even by subsequent heating; this results, accordingly, in unwanted clogging of the hotmelt glue gun, which cannot be eliminated even by heating.
In terms of their processing properties in corresponding hotmelt adhesive application apparatuses, such as hotmelt glue guns or the like, the reactive hotmelt adhesives described above are disadvantageous, since after corresponding use of the relevant equipment and after curing of the adhesives, they cannot be readily removed from this equipment.
As a result, therefore, reactive hotmelt adhesives do not always have the desired storage and processing properties, particularly with regard to their application in hotmelt glue guns.